Support visiting compressed image files

* lisp/image-mode.el (image-toggle-display-image): Support
visiting compressed image files which are uncompressed by
jka-compr.el.  (Bug#37330)

lisp/image-mode.el

@@ -720,6 +720,11 @@ was inserted."
 				     archive-superior-buffer))
 			   (not (and (boundp 'tar-superior-buffer)
 				     tar-superior-buffer))
+                           ;; This means the buffer holds the contents
+                           ;; of a file uncompressed by jka-compr.el.
+                           (not (and (local-variable-p
+                                      'jka-compr-really-do-compress)
+                                     jka-compr-really-do-compress))
                            ;; This means the buffer holds the
                            ;; decrypted content (bug#21870).
                            (not (and (boundp 'epa-file-encrypt-to)